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ZJ In-tank Fuel Pump Bypass

#1 User is offline   Rollbar 

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Posted 30 September 2007 - 04:13 PM

Ok here it is, the Swampy Bypass Write up...

***A word of warning, this write-up is my experience and is for discussion purposes only. If you choose to make similar modifications to your vehicle, they are at your own risk. Please take all appropriate precautions, especially with gasoline and any sources of ignition.***

The first thing you want to do is make sure that your fuel pump is the problem. That means eliminate all other possibilities. Change the fuel filter first. Then go to the fuel rail.. On the driver's side of the engine there is a Shraeder valve. Get a fuel pressure tester from Auto Zone or a similar parts store. (They'll rent it to you if you want.) You should have 39 pounds of fuel pressure with the ignition in the "on" position.

If you do not, locate the vacuum hose to the fuel pressure regulator. It's the round thing on the drivers side of the engine at the rear of the fuel rail on 93-95 models. With the engine running, pull the line. The engine should continue running. Then reinstall the line. If the engine stumbles, your regulator could be bad. On 1996-present models, the regulator is on the canister. Check it using the same method. It's just harder to do since you have to drop the gas tank.

If your regulator checks out okay or you couldn't get your engine running to check it, do one more simple test just to make sure....

Take a cup of gasoline... Pour a small amount down the throttle body. Get someone to start the engine. If it starts, pour a little bit more. If it keeps running then wait. If it stalls without gas. it is probably your fuel pump.

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Here is a picture of it installed on my rig. I got it from Jegs. It is part # 121-2225.

Then cut a hole in the floor. You can drop your tank if you want.

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Be extremely careful - your fuel lines are under there.

Then remove the stock canister which is visible in the picture.
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To remove it, you'll need a large screw driver. (Put it on the ridge and tap the cap loose.) Go under the Jeep and find the plug for the fuel pump and unplug it. Pull off the fuel lines and remove the canister. (If you are going to cut the hole, measure 18" from the tailgate trim and 18 inches from the drivers side wall and drill a large hole. Be very careful. You should be able to see the canister and trim it out accordingly.)

With the canister out, set it on a work surface. Be careful of the fuel level sender.. It can be popped off with a screw driver. It will take a while, but carefully open the top of the canister. It is obvious how to do it but be careful not to break the clips. (This may require two people but I did it on my own.)
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When the canister is cracked open, you will see the pump. Open the bottom as well to access the in-canister fuel filter. Clean that well.
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Cut the thin fuel line that holds the pump in and pull it out. Disconnect the wires and take them with you.
It should look like this.
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Test the pump on your battery one more time just to be sure it's bad. Now that you are positive the pump is crap, throw it as far as you can...

Take your new pump and attach some short wires to it. Test it on the battery, but not for long - running the pump dry for any length of time will damage it. Once you are sure the new pump is good proceed.

Insert a piece of fuel line into the top of the canister and thread it to the bottom of the canister. Connect the fuel line to the in-canister filter.
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Reinstall the canister, fuel lines and feed the plug down. Then you are ready for the next step.

Crawl under the Jeep. You will see a fuel filter canister on the driver's side (93-95). Follow the fuel line to the unit body rail directly in front of your control arm.

Cut the fuel line. You want to remove about 7 inches or so. Put the fuel line on both sides of the pump and slide it over the stock hard line. Use four hose clamps to tighten it up, but do not crush the stock fuel line. Mount the pump to the inner unit body rail. While you are at it, make a small jumper with a loop on both sides and ground the pump to one of the mounting screws.

Take another piece of wire and run it along the fuel line to the plug that you unplugged earlier. The #1 location on the wire is the fuel pump feed. (I am not going to tell you a color because it may be different.) Take a test probe and find the one that's hot when the key is on. On mine it's red with a tracer. Cut the wire in half. On the engine side of the wire, crimp the lead and run that wire to your pump positive side.

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Here is a picture of how the wire runs back up the fuel line.

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Make sure all connections are tight and use dielectric grease on electrical connections. (Remember, don't over tighten the fuel lines.) Check for any fuel leaks before you fire it up you should be done....

Note the pump makes a noticeably whine. (Typical to any high performance fuel pump.) It can be quieted down by isolating it from the frame with some type of rubber grommets or something.. You are on your own with that one.

If you have a 96 or newer ZJ/WJ, it's a little different for you. You will need an in-line fuel pressure regulator and it gets a lot more complicated.

Author:
Swamp Boy
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#2 User is offline   eddyrios 

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Posted 20 December 2007 - 08:24 PM

Great Write up!! This Mod is easy to do. I was pressed for time when I did this. Instead of ordering an MSD FP I went to local auto parts store and found an external fuel pump for a 1988 Lincoln Towncar 5.0. Works great!

#3 User is offline   Rollbar 

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Posted 20 December 2007 - 08:27 PM

Did U do it as the post suggests or did U just install the pump & let it suck through the old pump/system?
*MY CJ IS YOUR yJ's DADDY*

*Who Needs A Stinking Manual When You Have A Fat Wallet For Tech Support!*

*What man is a man who does not make the world better*

Support the Central Florida Bible Camp for kids

'65 CJ5 Navy; '74 CJ5; '80 CJ7; '84 CJ8; '86 CJ7
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#4 User is offline   eddyrios 

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Posted 20 December 2007 - 10:32 PM

no...removed the old internal FP and replaced with a fuel line, as the post shows. Thanks

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